1. Field of the Invention
The present invention relates to a carrier device in an automatic transmission, and, in particular, to a carrier device suitable for application as a carrier for an underdrive mechanism section in an automatic transmission used in a FF (Front Engine/Front Drive) vehicle wherein the underdrive mechanism section is positioned on a countershaft.
2. Description of the Prior Art
Recently, the applicant of the present invention proposed an automatic transmission, as disclosed in Japanese Laid Open Patent No. SHO-62-93546, which comprises a torque converter and a main transmission mechanism section arranged on an input shaft which is aligned on an engine crank shaft, an underdrive mechanism section arranged on a countershaft positioned in parallel on the input shaft, and a counterdrive gear and a counterdriven gear mounted on the center part in the axial direction to transmit power from the main transmission mechanism section to the underdrive mechanism section.
The underdrive mechanism section of the automatic transmission (additional transmission section) has a carrier boss section which engages on the countershaft through a spline, and the counterdriven gear is supported on the carrier boss section through a bearing. Also, the countershaft is provided with an annular protrusion which receives a thrust force and is constructed with almost the same diameter over its entire length. A large thrust force which is caused by the counterdriven gear comprising a helical gear is received only at the annular protrusion.
However, in the automatic transmission, the countershaft is positioned on the highest portion of three shafts, including the input shaft and the front axle shaft, and the dimension in the axial direction is largely controlled by the restraints from the vehicle load such as the side frame and the like. Because the carrier is separated from the countershaft, the dimension in the axial direction is large, and a problem arises in the loadability of the vehicle.
In addition, because the carrier is separated from the countershaft, it is difficult to supply the lubrication oil to the carrier cover from the shaft, and the supply of oil to the planetary gear is inadequate. This causes a problem with the durability of the planetary gear.
Further, because the large axial force from the counterdriven gear and the like is received only on the annular protrusion on the countershaft, a problem is produced with respect to the strength of the annular protrusion part. If the annular protrusion is thickened the increase in length in the axial direction becomes a problem.